Systems and apparatus for measuring the concentration of analytes in a sample have been developed using a number of analytical techniques such as chromatography, spectroscopy, and mass spectrometry. In particular, mass spectrometry is often the technique of choice to achieve sensitivity for trace and ultra-trace analysis in which the analyte concentration may be as small as parts per billion (ppb) or sub-ppb such as parts per trillion (ppt). For example, commonly assigned U.S. patent application Ser. Nos. 10/086,025 and 10/094,394 disclose automated analytical apparatuses that measure contaminants or constituents present in trace concentrations, the full disclosures of which are hereby incorporated by reference for all purposes.
Trace contaminant metrology (TCM) and chemical composition metrology (CCM) tools, both available from Metara Inc. of Sunnyvale, Calif., rely on an electrospray ionization time-of-flight mass spectrometer (ESI TOF MS) for the measurement and quantitation of analytes. Commercial ESI TOF MS instruments are not suitable for measurement of trace metals in industrial process solutions, for example those used in the semiconductor industry, due to interfering contamination that is introduced from component parts and due to degradation of trace contamination signal strength that can be caused by contamination build up in certain locations along the sample pathway. With continued sampling and analysis, contaminants from the ESI TOF MS system and residue from the process solution may accumulate in the sampling and analysis pathway, increasing inaccuracy, lowering spectrometer resolution, and further reducing sensitivity for trace contamination measurement. In order to acquire high resolution data with high sensitivity, a clean and easily maintained mass spectrometer system is required.
Accordingly, apparatus modifications and methods for instrument induced contamination reduction and signal optimization are essential for successful inline and automated chemical analysis of trace contamination.